1. Field of the Invention
This invention relates generally to control of a motor vehicle driveline, particularly to control during a tip-in of a driveline that includes a dual clutch automatic transmission.
2. Description of the Prior Art
During normal operation of a dual-clutch automatic transmission the driven input is connected to the transmission output shaft through gears. When the undriven input is preselected in a gear position in preparation for an anticipated gear ratio change, it is possible for driveline oscillations to cause an audible click-clack sound, during tip-in events. That sound is the result of oscillations in driveline torque and speed causing speed and torque reversals on the transmission components that are driveably connected to the transmission output but not connected to the engine.
Because the undriven input shaft is connected to the output when the next gear is preselected and before its connection to the engine, the meshing helical, preselected gears produce axial motion within the transmission on the undriven shaft. Because the input clutch corresponding to the preselected gear is not applied under these conditions, the entire shaft is free to move axially. When the amplitude of this motion exceeds the axial lash of the system, an impact occurs resulting in an audible output. The resulting sound is described as click-clack. As the driveline oscillates, the lash is taken up on both sides of the gear train.
In general, for good drivability the desired drive line response will be smooth and free of oscillations. To achieve this end, it is necessary to control the energy imparted into the drive line. Energy that is not converted to vehicle acceleration is dissipated through torsional oscillations until that energy is recovered by the clutch, accelerating the vehicle. The coordination of engine and clutch torques is of critical import when managing drive line energy.